1. Field of Invention
The present invention relates to a solid electrolytic capacitor having a conductive polymeric compound as a solid electrolyte, and more particularly to a solid electrolytic capacitor that has been improved for better withstand voltage characteristics, and a method for producing the same.
2. Background of Art
Electrolytic capacitors comprising a metal having a valve action like aluminum and the like can obtain smaller size and higher capacitance by way of changing the shape of a valve action metal used as an anodic electrode to be an etched foil and the like so as to enlarge the surface area of a dielectric material, and thus are in widespread general use. In particular, solid electrolytic capacitors comprising a solid electrolyte as an electrolyte have features of smaller size and higher capacitance and also have a low equivalent series resistance.
Examples of the known solid electrolytes used for a solid electrolytic capacitor include a conductive polymer having a high conductance and a remarkable adhesivity to the oxide film layer of the anodic electrode. Examples of the known conductive polymers include polyaniline, polythiophene and polyethylenedioxy thiophene.
In particular, polyethylenedioxy thiophene (hereinafter, “PEDOT”) has received attention as a conductive polymer capable of having greater withstand voltage because PEDOT can have greater withstand voltage relative to the thickness of an oxide film. A capacitor comprising the PEDOT is fabricated by way of a chemical oxidative polymerization in the following manner.
Namely, a capacitor element is formed by the anode and cathode electrode foils wound together with an intervening separator, and the capacitor element is impregnated with a solution containing EDOT and oxidizing agent, and is heated to form a PEDOT polymeric layer between the two electrode foils such that a solid electrolytic capacitor is formed. One such solid electrolytic capacitor is described in Japanese Laid-open Patent Publication No. H09-293639.
Unlike a conventional electrolytic solution capacitor, this type of solid electrolytic capacitor has a poor capacity to form an oxide film, and thus has limited withstand voltage characteristics. Accordingly, an electrolytic capacitor has been suggested that employs both electrolytic solution and solid electrolyte as electrolyte such that an oxide film formation capacity of the electrolytic solution is retained while remarkable characteristics of solid electrolytic capacitors are maintained. One such electrolytic capacitor is described in Japanese Laid-open Patent Publication No. 2000-021689.
This type of solid electrolytic capacitor has merely several tens of volts in rated voltage. In this context, the present invention is intended to provide a high-voltage solid electrolytic capacitor having a rated voltage of several hundreds of volts.